Can anyone explain this? I think to solve it we first need to discover the value of X and then the value of Y. But how can we solve for each two values with just one equation? That is why I thought it was C, because we had two equations and two variables. Or we dont need to solve for them separately???




One more thing, dont you think the quant part of GMATPREP 2 is much much easier than the quant part of GMATPREP 1??? Or maybe is that I have improved my quant skills since I did the first exam ;-p

I got a 49 with 8 errors four of which were stupid mistakes (specially three of them).

Thanks

Luci - this one is tricky, and it lies in the question stem itself.

No. of Video Cameras produced in 1993 = 1000
Assume 'a' be the increase in no. of video cameras in 1994,

So x = (a/1000)*100 or a = 10x

Similarly assume b be the increase in no. of video cameras in 1995,

So y = (b/(1000+10x))*100 or b = ((100+x)/10)*y

Now total no. of video cameras in 1995 = 1000 + a + b = 1000 + 10x + ((100+x)/10)*y...(1)

Solving (1)

10(100+x) + ((100+x)/10)*y

= (100+x)(10+y/10) = (100+x)(100+y)/10 = 10000+10(x+y) + xy/10 = 10(1000+(x+y)+xy/100)

Now statement (2) gives us the value of the expression (x+y)+xy/100. Hence it is sufficient.

GMAT 2007

Amazing explanation GMAT 2007. Thanks a lot. Although I think it is a very tough problem, I dont think I will be able to solve it in 2 minutes. Not because the logic of the question stem, which is brilliant how you did it, but all the factoring you have done seems too tough to me. This is one of those to try a good guess and keep going I think, :-).

We could also do this problem the following way:

1993 = 1000 video cameras
1994 = 1000*(1+x/100)
1995 = 1000*(1+x/100)(1+y/100)

group the equation for 1995
1995 = 1000*(1+x/100+y/100+xy/10,000)

Evaluate the statements

Statement 1) This is insufficient because we need the values for x and y

Statement 2) is the further simplified from the equation we have x+y+xy/100=9.2, which can be simplified to fit our rephrased equation

1995 = 1000*(1+x/100+y/100+xy/10,000) = 9.2
1+x/100+y/100+xy/10,000=.0092 (divide both sides by 1000)
x/100+y/100+xy/10,000=.0092-1=.9908 (subtract 1 from both sides but ignore the negative sign because you cannot sell negative video cameras)
x+y+xy/100=99.08 (after multiply throughout by 100)

well played.